1. Field of the Invention
The present invention relates to a method for forming a carbon protective film and a method for producing a magnetic recording medium, a magnetic recording medium and a magnetic recording/reproducing apparatus, that are used in hard disk drives and the like.
Priority is claimed on Japanese Patent Application No. 2007-004395, filed in Japan on Jan. 12, 2007, the contents of which are incorporated herein by reference.
2. Background Art
In the field of magnetic recording media, particularly magnetic disks, a remarkable improvement in recording density has recently been made and, in particular, the recording density has increased at a remarkable rate of around 100 times in ten years. There are various technologies that support such improvement in the recording density and one of key technologies includes a technology of controlling sliding characteristics between a magnetic head and a magnetic recording medium.
Generally, since a CSS (contact start-stop) system called Winchester system, in which contact sliding/head floating/contact sliding between a magnetic head and a magnetic recording medium constitutes a basic action, became popularly employed in hard disk drives, sliding of the head on the recording medium became unavoidable and thus a problem relating to tribology between the magnetic head and the magnetic recording medium is a fatal technical problem at present. Therefore, abrasion resistance and sliding resistance of the surface of the medium play an important role in reliability of a magnetic recording medium, and strenuous efforts on the development and improvement of a protective film, lubricating film, and the like to be laminated on a magnetic film have been exerted.
As the protective film of the magnetic recording medium, those made of various materials are proposed. From an overall viewpoint of film forming properties, durability, and the like, a carbon film is mainly employed. The carbon film is usually formed by a sputtering method and the conditions upon film formation are vividly reflected in corrosion resistance of the carbon film or CSS characteristics and are therefore very important.
It is preferred to decrease the flying height of the magnetic head and to increase the rotation speed of the medium so as to improve the recording density, and thus it has become required to impart higher sliding durability to the magnetic recording medium.
It has become required to decrease the thickness of the protective film as thin as possible, for example, a thickness of 100 Å or less, so as to increase the recording density by decreasing spacing loss. A thin and tough protective film, not to mention smoothness, are strongly desired.
However, in a carbon protective film formed by a conventional sputtering film formation method, when the thickness of the film is decreased as thin as possible, for example, 100 Å or less, the durability thereof sometimes becomes insufficient.
Therefore, as a method capable of forming a carbon protective film having a high strength as compared with the case of using a sputtering method, a method employing a plasma CVD method (for example, Japanese Examined Patent Application, Second Publication No. Hei 7-21858; Japanese Unexamined Patent Application, First Publication No. Hei 7-73454) is widely used.
However, in the methods as described in said Japanese Patent Applications (Publication Nos. Hei 7-21858 and Hei 7-73454) in which the carbon protective film is formed using the plasma CVD method, carbon is accumulated not only on the surface of a substrate, but also on the exposed surface in a film formation chamber, for example, the surfaces of electrodes and the like in a film formation device. When the accumulation amount of carbon on the exposed surface in the film formation chamber increases, the film made of accumulated carbon is peeled from the exposed surface due to internal stress. When particles of carbon produced by peeling adhere on the surface of the substrate, there arises a problem that protrusions are formed on the surface of the carbon protective film to cause local film thickness abnormality, thus resulting in product failure. Particularly, when the carbon protective film is formed using the plasma CVD method, the resulting film made of carbon has high hardness and also has high internal stress as compared with the case of forming the carbon protective film using a conventional sputtering method. Therefore, a lot of carbon particles are generated to cause a problem such as film thickness abnormality described above.
A method of removing a carbon film accumulated in a film formation device through ashing using oxygen plasma (for example, Japanese Unexamined Patent Application, First Publication No. Hei 11-229150; Japanese Unexamined Patent Application, First Publication No. 2002-025047) has been proposed so as to prevent such above-mentioned generation of particles.
Also, a method of suppressing peeling of an accumulation on electrodes by roughening the surfaces of the electrodes (for example, Japanese Unexamined Patent Application, First Publication No. 2006-173343) so as to prevent the generation of particles in a treatment chamber in a plasma CVD apparatus has been proposed.
Further improvement in the smoothness of the surface of a magnetic recording medium so as to further improve the recording density of the magnetic recording medium has recently been desired. However, even in the case of using the methods described in said Japanese Patent Applications (Publication Nos. Hei 11-229150, 2002-025047 and 2006-173343), there is a problem that the generation of particles cannot be sufficiently decreased and it is difficult to enhance flatness of the surface of the magnetic recording medium. Therefore, a method capable of decreasing the generation of particles in the plasma CVD apparatus is desired more than ever.